1. Field of the Invention
The present invention relates to automobile-mounted telephone devices which realize telephone communication with other telephone devices via a radio circuit and, more particularly, to apparatus with an automatic answering or receiving function which inhibit excessive use of an automobile battery by the answering or receiving function.
2. Description of the Prior Art
FIG. 1 shows one example of automobile telephone devices having such automatic answering or receiving function. As shown in FIG. 1, the automobile telephone device mainly includes a transceiver unit 1 and control unit 2. Transceiver unit 1 is usually built in the rear trunk of the automobile, and includes power supply 11, automatic receiving or answering unit 12, first control module 13, radio unit 14, and audio unit 15. Control unit 2 is usually installed near the seat of the automobile, and includes main switch 21, display unit 22, second control module 23, key pad unit 24, telephone receiver 25, a telephone transmitter 26 and speaker 27.
The operation of the telephone device shown in FIG. 1 will now be described briefly. First, an incoming call signal from a different telephone device is received by antenna 4 and applied to first control module 13 via radio unit 14. First control module 13 is responsive to that signal to deliver a signal to second control module 23 of control unit 2. Thus second control module 23 drives speaker 27 to generate a ringing tone. If the handset (not shown), which includes telephone receiver 25 and telephone transmitter 26, is taken off the hook in response to that ringing tone, this operation is detected by second control module 23 which then delivers a signal indicative of this detection to first control module 13. First control module 13 enables audio unit 15 to operate. Thus telephone communication is possible via antenna 4, radio unit 14, audio unit 15, telephone receiver 25, and telephone transmitter 26.
As well known, automatic answering or receiving unit 12 is adapted to automatically receive and respond to an incoming call from a different telephone device by allowing the caller to hear messages recorded beforehand on an endless tape or in an IC memory, and then by recording the contents of the caller's business even when the driver of the automobile on which the telephone device 12 is mounted leaves the automobile. The driver can confirm the contents of the caller's message thus recorded when the driver returns to his automobile. The fact that there was an incoming call from a different telephone device can be indicated by display unit 22.
In order to operate automatic answering or receiving apparatus 12, as mentioned above, first, main switch 21 of control unit 2 is turned on to operate power supply 11 of the automobile telephone device. Key pad unit 24 of control unit 2 is then used to perform a predetermined operation to thereby drive the telephone device.
The automobile telephone device having such automatic receiving or answering device 12, if device 12 is set in an active state, as mentioned above, consumed currents flow from automobile battery 3 to respective elements of the telephone device via power supply 11 each time there is an incoming call. This occurs even when the driver has stopped the engine and has left his automobile. Therefore, in the worst case, battery 3 voltage may drop so greatly that the driver cannot restart the engine.